To solve the problem of insufficient response accuracy for dynamic equivalence system after power system operating conditions change, this paper proposes a global representation heuristic dynamic programming (GrHDP)-based dynamic equivalence method. Based on the model obtained by coherency equivalents method, a dynamic compensation block based on GrHDP is added to the boundary of the equivalent model, which can compensate the dynamic response difference between the equivalent system and the original system. Therefore, it can accurately track the original system dynamic characteristics. Case study is undertaken on a 10-machine 39-bus power system. Simulation results show that the equivalent model obtained by proposed dynamic equivalence method can more accurately track the original system dynamic characteristics than that obtained by the coherency equivalents method under different operating conditions and fault locations. This work is supported by National Natural Science Foundation of China (No. 51529701).